Systemic lupus erythematosus (SLE) in humans is characterized by autoantibody production to a variety of self-proteins. In an effort to clear the subsequent antibody-antigen complexes from tissues such as the skin and kidneys, the resulting inflammatory response produces a number of oxidative by-products, such as free radicals, that posttranslationally modify self-proteins. The result of the modification of these self-proteins is 1) that previously non-immunogenic proteins are now immunogenic, 2) they are recognized and processed differently than their un-modified forms and 3) they alter cell signaling. Together, these factors contribute to the generation of autoimmune pathology. During the inflammatory process that occurs with lupus, protein methylation reactions, such as the conversion of aspartic acid to isoaspartic acid and arginine methylation, increase. The enzymes that mediate protein methylation reactions require the methyl donor S-adenosyl- methionine. Isoaspartic acid formation is the result of the deamidation of asparagines or the isomerization of aspartic acid to isoaspartic acids. Arginine methylation is catalyzed by various protein arginine methyltransferases. The proposed studies will examine the mechanisms behind how these protein methylation reactions alter autoimmune disease and pathology. We will quantitate the levels of protein methylation in lupus patients by measuring the levels of isoaspartic acid and arginine methylation in resting, activated, and apoptotic T cells and monocytes. We will determine how protein methylated self-antigens are processed for antigen presentation by digesting the known modified lupus autoantigens snRNP, histone H2B, and symmetrical dimethylarginine Sm D1 and D3 with enzymes involved in antigen processing and apoptosis. Finally, we will use two mouse models, both on the lupus-prone MRL/lpr background, to determine how increased isoaspartic acid levels and protein arginine methylation affect lupus disease and pathology. Results of these studies will be helpful in determining immunotherapies for the modulation of autoimmunity. PUBLIC HEALTH RELEVANCE: PROJECT NARRATIVE Systemic lupus erythematosus (SLE) is a life-threatening disease, in which antibodies against self-proteins damage various organs. The self-proteins that are responsible for the initiation of SLE still remain unknown. We have shown that posttranslationally modified self-proteins render otherwise immunologically ignored self- proteins immunogenic thus potentially initiate disease.